Your example with the LED reminds me of a hack I did a few years ago. We had a flight computer on our rocket we were building to set the world altitude record, it was made super lightweight and the batteries were tiny coin cells. The computer had a couple of external status LEDs that blinked the state so we could see it from a safe distance. Well, we had a number of accidental launches while building the rocket pressure because we were working out the details of our launcher design. To conserve battery power, we did not arm the system until it was near full pressure, so if it launched unarmed then the deploy system would never be activated, and the rocket would crash. The hack solution was that I rewrote the software to use one fewer LEDs for status and the other one (that happened to be on an ADC pin) was repurposed as a launch detect light sensor. I used the light sensitivity of the LED as a trigger to arm the deploy system. When the rocket was on the pad, we put a shade over the LED that would pull away if the rocket ever launched prior to being armed. It worked like a charm. Necessity is the mother of invention!
Very few people seem to realise that LEDs work both ways and even fewer make use of it. They respond to the same wavelength they emit, something which I've used on ATE to check that the right colour - red, yellow or green - LED has been fitted in the appropriate position. Works with IRLEDs too and is made use of in some learning IR remotes.
EEVblog Honestly i don't see why they really need to bother. They probably will just because of the squeaky wheel principal, but really it is likely a non issue for >99% of the users. But what do I know?
Actually, it doesn't have to be a specific frequency, it just needs to be higher than a specific point. So it's not the infrared light from the flash, it's probably the uv ones.
The reason ARM processor is locking up might be because this temporary dip in voltage causes it to get lower than minimum voltage needed for correct operation, slowing down the switching speed of MOS transistors and hence causing timing violations ( setup time for flip flops) for the clock freq it is running at. The internal SRAMs might also loose the value they were holding at the time of dip if it drops below voltage needed for state retention (~ threshold voltage). All of this will cause state corruption for the processor logic and can cause the internal FSMs to hang up/get in wrong/bad state. Normally in a critical processor, there would be a watchdog timer to guard against such hangs and would cause a reset, but perhaps raspberry pi is too cost sensitive to have such a mechanism in place.
That's what I was thinking. I'd be interested in an experiment where a large bypass capacitor was connected near the ARM to the 1.2V bus, which might reduce the severity of the dip. I wonder if the lock-up would still occur.
Joe Tsai MichaelKingsfordGray , actually any supervisor which is onboard on same processor will also get corrupted and will fail to catch this case. Likely this broadcom chip would also be having a dedicated internal interrupt for watchdog timer, which the OS might have also enabled, but such a dip in supply will cause that too to get reset as well. I was referring to external watchdog supervisors which are usually part of companion power management ICs - you would find them in life critical applications. A little more detail here. www.maximintegrated.com/en/app-notes/index.mvp/id/4229 www.ti.com/lit/an/slva039/slva039.pdf
and it's also present on the Rpi B+ (but it doesn't seem to be anywhere as vital as the U16) as I was unable to cause any havoc by flashing the hell out of it ;)
I thought it would be a RFI or EMI of the flash circuit, but never expected that to be the cause. You can put black epoxy on a flip-chip too, there's no need for use older style bond wired chip. Thanks for upload.
This reminds of that episode of the Simpsons, Itchy & Scratchy Land - they stopped the killer robots using disposable cameras flashes. As Myth Busters would say - 'plausible!'
Hey Dave By an insane coincidence I was just checking out the work functions (en.wikipedia.org/wiki/Work_function ) of several elements yesterday , some people might be a bit confused as to why the UV light doesn't appear to be responsible for triggering the effect...and why the peak in the IR range might matter...and I think I've got the explanation...the thing here is that the Photoelectric effect as is normally taught in physics 101 tends to cover only the situation where you're trying to expel electrons from the surface of crystals of pure elements ... So if we were to calculate the minimum frequency for a photon to remove electrons from , say...pure silicon (best case work function 4.60eV ) we'd reach something like 270nm (UV) .. so yeah ... no peak of light, no matter how strong (amplitude) over 270nm (towards visible light) should be able to extract electrons from the surface of a pure silicon crystal... BUT! (skipping to microelectronics 101 (taking my trusty Sedra/Smith from the bookshelf!) We're talking about a semiconductor! there's no need to overcome the work function and extract electrons from the material , we just need to overcome the bandgap (This is equivalent to the energy required to free an outer shell electron from its orbit about the nucleus to become a mobile charge carrier -wikipedia) , and this takes FAR LESS energy (en.wikipedia.org/wiki/List_of_semiconductor_materials) ! Bandgap for silicon would be 1.12eV (I'm using Si as an example... it might not be Si but the orders of magnitude are mostly the same for most semi (check table above) ) would put the needed wavelength at 1.1micrometers (IR) So if we fire enough photons of shorter or equal wavelength than say 1.1 micrometers (again,Si only an example) to overcome the bandgap we should make something that shouldn't be conducting at that moment temporary into a conductor which is more than enough to cause all sorts of craziness in there (current should be proportional to amount of photons (amplitude)) Also a Flash Lamp emits something in the order of magnitude of a MILLION lumens (www.wolframalpha.com/input/?i=1000000lumen) over a few micro-seconds and lumens are only measured in the visible light range! ...so according to the spectrum graph you've shown the peak in IR would be even greater ...that's a LOT of IR photons which are probably over the bandgap energy and are probably making a semiconductor into a "short" (whose conductivity is proportional to the peak amplitude of the light)... What do you think EEVblog ? Diego Spinola (but you can call me Bruce ;) )
There is something what im wonder about, at 19:53 when dave flashs the pi the last time i have the impression that the pi goes off some microseconds before the flash is flashing.
Near IR has a lower frequency than visible light, so less energy than visible light. However, what's probably going on is that silicon is more transparent to infrared, so infrared light coming in through the back of the die can affect it.
Nope, the spikes are in the UV range and he has mislabeled the chart. The fact that dim blue light produces a more pronounced photoelectric effect than bright red light was one of the clues that originally gave Einstein the insight into working out what was going on.
LiamE69 I think it's labelled properly (in nanometers). I did a quick image search for "xenon spectrum" and all of them have lower-frequency light (IR) on the right, as opposed to how RF spectrum is normally plotted. They also all show that xenon has spikes in the IR part of the spectrum, but not in the UV part. I don't know how transparent silicon is to UV, but it is certainly transparent to (some?) IR.
Karl Koscher I did the same and looked up the spectrum of xenon lights as you can see on a post elsewhere here. Yes the spikes are in NIR. As for labeling I simply cannot see any in my video. I could see the figures but not the unit. As he talked about frequency I had it in my head that it was the units were THz, but he does say it is nm. That correction aside, it really is the UV doing it. The IR spikes will have a far smaller PE effect than the portion of the emissions in visible light which in turn will have a smaller PE effect than the portion of a xenon lights output below 400nm, which is small but significant.
InXLsisDeo Yeah, been there corrected that. Still it doesn't change the fact that the PE effect is a threshold effect. NIR doesn't produce a PE effect on any material I am aware of. Visible light does on some materials. Near UV does on most metal and as it is produced by a xenon arc it is the culprit here. Very high UV and beyond produces a PE effect on anything but is not produced by a xenon flash.
Dave, silicon is transparent to IR light, right where PN-junctions starts to loose sensitivity. So photons to blame are between 1050nm and 1100nm wavelength: silicon is somewhat transparent there and PN-junctions are still slightly sensitive.
Hey Dave! The infrared part of the spectrum can't be the light causing the problems. Infrared light has a lower frequency than visible light. Remember that frequency is inversely proportional to wavelength.
I would have assumed RFI, from the high voltage supply of the Xenon power supply... looks like I am wrong, and not would have expected the photo effect, which you have clearly shown even by cutting apart the 2222A transistor. Thanks for demonstrating!
Hey Dave, love the video; I was wondering what the deal with this was. I have to nitpick the physics a tiny bit, though. You're saying "energy" or "amplitude" when "intensity" is more correct. Yeah, a higher number of photons can collectively have a higher total energy than a lower number of photons, but when explaining the meaning of that wavelength/intensity graph the word energy should be used only in reference to the wavelength axis, not the intensity axis.
Maybe the high frequency pulse is the xenon trigger pulse and the second blip is the current through the lamp? you could check by measuring the time in between the pulses and comparing it to the time it takes for significant current to flow through a typical xenon lamp after it receives a trigger pulse.
Few years ago (back when I was just beginning with electronics) I did an experiment in which I have cut out the top of a TO-18 packaged transistor (just like you did) and stuffed IR LED inside. This way I've build working optocoupler. It was a crap but it worked.
At one of my collage courses ( measuring in electronics ) our profesor told us that IR spectrum of light is the most dangerous for semiconductors (i think we were doing something with " optocouplers " ) so this must be true! Thanks Dave for renewing my knwledge
It was probably said in a later video, but could it be that the Broadcom chip had browned out from the drop in voltage from the buck converter? And said brown out doesn't auto-reset it?
if possible could you revisit this? it looks like you actually covered some of the main arm chip as well when you covered it the second time. - cab you try just using a ir filter cut to fit the small chip or something else to confirm? obviously it seems like youve nailed it - but I am just curious. -murica
While I am not an expert, from what I have read I believe that this is an example of the photovoltaic effect, not the photoelectric effect as you say. To quote WIkipedia: "Instead, as it turns out, electrons are only dislodged by the photoelectric effect if light reaches or exceeds a threshold frequency". But as you say in the video, the effect here is a result of the spikes in the infrared, and people testing with high-intensity visible light have generated no reaction. As per Wikipedia, the photovoltaic effect doesn't have the same threshold. And it does occur in silicon, as it is the effect used for current generation in solar cells. I see that you have put various extra text on the video, but e.g the one 10:26 talks about total energy, where if it was the photoelectric effect it would also have a requirement for individual photon energies. At 11:53 you also talk about a specific frequency, where the photoelectric effect works with lower threshold frequencies.
My Raspberry Pi 2 B arrived this morning. A full kit with it too. Here's hoping and fingers crossed. Before I start, should I ut a blob of black silicone over the ic?
The energy needs to be above the work function for the material. So there isn't a *specific* wavelength that it works at, there's a boundary where it starts to work. Also uv is higher energy than optical and ir, so if the light enters from the side it'll probably be the uv.
a big gob of blue-tack in your hand can be used to dab off the remainder of the goop on your board. Thanks for the video - I totally thought it would have been the EM pulse from the high voltage discharge rather than the actual photoelectric effect. Brilliant!
Most intriguing, wonder how much knowledge can a mind contain before it runs away rampant? Or perhaps evaporating much of what we learn to create space for more information? Either way I find it interesting how history, physics and electronics play a direct role in the scheme of things and yet wonder helplessly how much more information I need to store in my mind before I go totally bonkers, plus I still have neither bought myself a decent multimeter nor a bloody meager scope. I am definitely certain that all of us require a sort of calibration to weigh the value of the knowledge we attain for the sake of validating its virtue. I believe it is the character not the quantity of information, for those who are eager to learn then they will learn beyond any caliber or measure. Interesting video, thanks Dave.
I've dealt with this effect a few times in 35 or so years, mainly with clear glass diodes injecting noise into analog circuits. While I believe that you have found the culprit, I would feel 100% confident (as opposed to 98%) if your test had also included the inverse test, (ie. masking everything but the I.C. in question). Still nice illustration of how a perfectly engineered product can be totally compromised by a little cost savings on a single I.C. device.
U16 is a problematic die level chip in the R-Pi2. My solution to this is to encase it with some black hot glue. This chip should have been covered when it was put on the board but QC now-days is non existent it seems. I have recreated the Xeon lock eccect by using different light sources from Xeon flashes to White Blue, and UV LEDs. Another effect also exists with the pi and that's the EMP Effect from devices that emit RF such as a cell phone or 2-way radio which will cause the Pi to lock up also. There is no RF shielding on the Pi so all sort of stray signals can get in and cause the pi to malfunction. Solution for this is to shield the pi IF your using it as a control device for a wifi repeater node you want to shield it from the wifi RF.
Hi Dave it is common problem with micro controllers for example we have same problem with STM32L series when it ramp up with specific sloop rate it hang up and no WDG work even
have you considered that the light from the might might be trensferred through tha circuitboard it self, and actually shining light on the chip from underneath?
I remember seeing a thing in a ZX Spectrum magazine in the 80's about how to turn a memory chip into a camera to connect to your speccy, think it was a memory chip anyway, it was a long time ago.
Yeah, the explanation given is wrong. A large number of photons emitted by the xenon flash have a frequency that corresponds to the energy of the bandgap of the semiconductor material. When these photons are absorbed by the semiconductor, electrons jump from the valence band to the conduction band, resulting in current flow, which screws with the voltages in the chip.
***** the smps chip might be self regulating for slowly (in most terms) ramping effects hence why bright light doesn't affect it, but the sudden immense pulse from the xenon flash is the quality, quantity and intensity slope required to break the regulation loop.
***** It has everything to do with the bandgap. The photoelectric effect is about electrons being given enough energy to escape from the surface of the metal (which we are only likely to observe in vacuum like Einstein's experiments were). This specifically relates to undoped materials, and the silicon in question is made up of doped p-n junctions. The photoelectric effect is slightly different theory to band gap physics. However, incident photons with energy greater than or equal to the band gap of the material will promote electrons to the conduction band from the valence band allowing current to flow. It's for this reason that silicon transistors become useless at high temperatures (Thermal distribution shifts to an emission spectra near the bandgap) because you end up with a large proportion of electrons in the conduction band effectively turning your transistor into a wire. Also, the intensity of the light doesn't have any effect on electron energy, but it does relate to the number of photons emitted.
InXLsisDeo Looking at the transmission spectra of silicon, it is about 55% transmissive at UV frequencies. So having said that, we can expect that roughly 45% of photons at a UV frequency are absorbed and will most likely contribute to any current generated or simply thermalise (shed excess energy through lattice vibrations/phonons) down to lower bands.
So, would it fix the problem if you would put some of that black stuff he showed around that tiny chip? And would you need a lot like from that blue stuff or would a small amount be fine?
I think you needed so much bluetack because there are 2 exposed chips on the board, the second one being right behind the HDMI port. You only eliminated the photo electric effect after you had covered both chips with blue tack. This is of cause just a guess as to why you needed so much, what do you think?
Hi, I think there's another chip-scale package near the HDMI-Connector. It wasn't covered by Blue Tag on the first trial, but covered by Blue Tag on the second trial. Maybe that's the real culprit and not the switch mode regulator ?
I am relitively newbie in electronics, but can you add a capacitor on that line to keep it stable and compensate that time the voltage drops down? At least theoretically am i right?
is this the same thing that is supposed to brake out satellites if there is a big solar flare? would putting some black tape over the exposed chip protect against this effect?
Hi All Could the problem be in the circuitry used to drive the camera's xenon bulb - electrical impulse rather than a light/photon impulse issue? This could explain why the blue putty didn't work . . .
Great video!!!! Got my brain churning!!! Some further ideas come to mind: You could try a UV LED to see if it it UV energy. Another thought: Could the actual problem be the EM pulse from the photo-flash, not the actual light. I postulate this because the board reacted in a similar manner when flashed from behind.
Ok, someone posted on FB that they took a flash picture of their 3D printer with their phone, and it crashed. Is it possible the "flash" on newer phones, a Samsung S10, is closer to a Xenon flash?
I like Dave's solution, put some blue tac on it!, it's reminiscent of the fix on the ZX81 Ram expansion module being loose and causing the ZX81 to crash. A kid used blue tac to solve the issue and Sir Clive himself demonstrated the blue tac fix at a trade show!
actually... I think you're only thinking about the classic photoelectric example of ripping of electrons from the metal surface(work functions)... However the Bandgap energy on semiconductors allows for much lower energy photons to be causing charge carriers (free electrons in the lattice) to "appear" and thus make a semi-conductive junction to ...well... conduct when it shouldn't if you take the bandgap for pure Si 1.11eV (as an example... the doped junction in that IC has probably a lower bandgap still) and compare it to it's work function 4.60eV you'll see that IR and visible light CAN cause it to conduct when it shouldn't (so yeah, not because of positive "carriers" but negative ones)
Diego Spinola yep...that's actually true...i remember cracking old TO-3 packages and measuring that the die produced current when exposed to light...still an interesting problem...I would be curios to see what happens if one shines an uv LED straigt into the chip, though
No, no, no! Dave, please, don't explain something simple like this the wrong way! D: The energy of the photon is E=hf, meaning that a higher frequency will put more kinetic energy into the electron, increasing *voltage*. The number of photons, however, determines the number of emitted electrons, which increases *current*. There is also not a specific frequency required in order to emit an electron, it's a *minimum frequency*. The infrared spikes in the xenon spectrum would therefore (if they are above the minimum frequency at all) create a spike in current, but it would be at a very low voltage compared to the electrons emitted by the photons of visible frequency.
It might be the IR as you mentioned. Silicon is transparent to IR. It probably is not getting to the chip from the underside. It is probably going right through the top face. Thanks for the excellent video. On a side note radio shack black plastic project boxes are somewhat transparent to IR as well.
Would it be possible to add a Capacitor so that when the regulator drops out the cap provides power for the few ms it takes to recover? I understand that's not best solution, preventing it from happening would be better, but could it be an option, perhaps for people who want to bodge something in there...
I was thinking of buying one of these to run as a media centre. But I really dislike Kodi, something about it irks me the wrong way and I hate using it. Better options?
Quick question out of curiosity. If the regulator is recovering so quickly could the problem also be solved by more decoupling caps on the inputs to whatever is locking up?
aftertwotoo Perhaps, but that would be a poor fix, as you shouldn't rely on the regulator to recover from such a thing. Much better to simply stop the problem from happening in the first place.
Yep, but it clearly blocked it. I wonder if black enamel paint would work. Adding to that, the HF spike he mentioned was from the loop of ground. I assume he meant the flash cap dumping all the current made some RF.
now i am wondering, redoing all of the board is not an option. A blob of "blackness" could do the trick. But you showed that there is a drop in power during that flash and the processor stops working. What if they put an elco ( or how it is called in english ) in that spot so that there won't be a drop in power. Theoraticly the processor could be working all the way through while the power regulators recovering and bringing all back to normal. Could that also do the trick?
Если кто-то застал те времена, когда в старых микросхемах BIOS было заклеенное скотчем окошко на кристалл. Информация CMOS сбрасывалась путем подачи света в окошко на микросхеме, а не перемычкой как сейчас -)
Never tough I would see bearchip with out plastic package, especially BGA... Just wondering if its possible to make video for LIN and CAN communication's. Would be nice because they are widely used this days in many communication systems and mostly in the automotive manufactures. I can make video of my own but I doubt it would be any close to the level of your videos Dave. Anyway keep up the good work! P.S. Raspberry rocks I use one to run my home FTP server and wake up by the network my home mighty xeon server that I run ESXI and some unix and linux virtualized OS systems on it. Saves a lot of energy rather running that server 24/7, just waking it up when I need it :) And the raspberry consume only like what 5w/h?
Hi! Nice to see you got the new Raspberry Pi 2 Model B. I love it! I got one myself. I have experience with the Raspberry Pi and blog tutorials to get started with it! I also blog Arduino, C/C++ - Tutorials and projects I make. I am so sorry for this self advertising, but my blog is fairly new and I would love to see you on my blog. I might help you. But for now… I follow you! Thanks for reading!
Your example with the LED reminds me of a hack I did a few years ago. We had a flight computer on our rocket we were building to set the world altitude record, it was made super lightweight and the batteries were tiny coin cells. The computer had a couple of external status LEDs that blinked the state so we could see it from a safe distance. Well, we had a number of accidental launches while building the rocket pressure because we were working out the details of our launcher design. To conserve battery power, we did not arm the system until it was near full pressure, so if it launched unarmed then the deploy system would never be activated, and the rocket would crash. The hack solution was that I rewrote the software to use one fewer LEDs for status and the other one (that happened to be on an ADC pin) was repurposed as a launch detect light sensor. I used the light sensitivity of the LED as a trigger to arm the deploy system. When the rocket was on the pad, we put a shade over the LED that would pull away if the rocket ever launched prior to being armed. It worked like a charm. Necessity is the mother of invention!
Very few people seem to realise that LEDs work both ways and even fewer make use of it. They respond to the same wavelength they emit, something which I've used on ATE to check that the right colour - red, yellow or green - LED has been fitted in the appropriate position. Works with IRLEDs too and is made use of in some learning IR remotes.
Graham Langley
Is in electrical hobby very common info that led can be used as a sensor, tons of video and tutorials out there about leds as sensor.
Graham Langley Using the wavelength to test the color is really clever. Nice!
peter w
OK, so I got it wrong with the "very few people...". I first did this at a firm I was working for back in the late 80s.
This is a great one Dave! I imagine that a little blob of potting will immediately be added there to new units. DOH!
Fran Blanche Yep, they will certainly do that. By far the easiest option. Maybe adds a 5-10c per board or something for the labour.
EEVblog
And all after the fact.... It never ceases to amaze how they cut corners to optimize products these days at the expense of common sense.
Fran Blanche I doubt they did this deliberately, I just think the designers didn't think of the possibility. Lesson learned quite publicly!
EEVblog
Honestly i don't see why they really need to bother. They probably will just because of the squeaky wheel principal, but really it is likely a non issue for >99% of the users. But what do I know?
EEVblog
Certainly not deliberate.... but also not to be repeated I suspect.
Actually, it doesn't have to be a specific frequency, it just needs to be higher than a specific point. So it's not the infrared light from the flash, it's probably the uv ones.
I always appreciate how happy DaveCAD is! Just something about that smiley face with the bright sunny post-it!
The reason ARM processor is locking up might be because this temporary dip in voltage causes it to get lower than minimum voltage needed for correct operation, slowing down the switching speed of MOS transistors and hence causing timing violations ( setup time for flip flops) for the clock freq it is running at. The internal SRAMs might also loose the value they were holding at the time of dip if it drops below voltage needed for state retention (~ threshold voltage).
All of this will cause state corruption for the processor logic and can cause the internal FSMs to hang up/get in wrong/bad state.
Normally in a critical processor, there would be a watchdog timer to guard against such hangs and would cause a reset, but perhaps raspberry pi is too cost sensitive to have such a mechanism in place.
the internal flying spaghetti monster hang up?
That's what I was thinking. I'd be interested in an experiment where a large bypass capacitor was connected near the ARM to the 1.2V bus, which might reduce the severity of the dip. I wonder if the lock-up would still occur.
Joe Tsai MichaelKingsfordGray , actually any supervisor which is onboard on same processor will also get corrupted and will fail to catch this case.
Likely this broadcom chip would also be having a dedicated internal interrupt for watchdog timer, which the OS might have also enabled, but such a dip in supply will cause that too to get reset as well.
I was referring to external watchdog supervisors which are usually part of companion power management ICs - you would find them in life critical applications.
A little more detail here.
www.maximintegrated.com/en/app-notes/index.mvp/id/4229
www.ti.com/lit/an/slva039/slva039.pdf
U16 isn't the only bare chip on there. U8 (tiny thing, right next to the HDMI port) is the same construction.
and it's also present on the Rpi B+ (but it doesn't seem to be anywhere as vital as the U16) as I was unable to cause any havoc by flashing the hell out of it ;)
I thought it would be a RFI or EMI of the flash circuit, but never expected that to be the cause. You can put black epoxy on a flip-chip too, there's no need for use older style bond wired chip. Thanks for upload.
IR is low frequency compared to the visible light. High frequency are UV and X-rays
This reminds of that episode of the Simpsons, Itchy & Scratchy Land - they stopped the killer robots using disposable cameras flashes. As Myth Busters would say - 'plausible!'
Hey Dave
By an insane coincidence I was just checking out the work functions (en.wikipedia.org/wiki/Work_function ) of several elements yesterday , some people might be a bit confused as to why the UV light doesn't appear to be responsible for triggering the effect...and why the peak in the IR range might matter...and I think I've got the explanation...the thing here is that the Photoelectric effect as is normally taught in physics 101 tends to cover only the situation where you're trying to expel electrons from the surface of crystals of pure elements ...
So if we were to calculate the minimum frequency for a photon to remove electrons from , say...pure silicon (best case work function 4.60eV ) we'd reach something like 270nm (UV) .. so yeah ... no peak of light, no matter how strong (amplitude) over 270nm (towards visible light) should be able to extract electrons from the surface of a pure silicon crystal...
BUT! (skipping to microelectronics 101 (taking my trusty Sedra/Smith from the bookshelf!)
We're talking about a semiconductor! there's no need to overcome the work function and extract electrons from the material , we just need to overcome the bandgap (This is equivalent to the energy required to free an outer shell electron from its orbit about the nucleus to become a mobile charge carrier -wikipedia) , and this takes FAR LESS energy (en.wikipedia.org/wiki/List_of_semiconductor_materials) !
Bandgap for silicon would be 1.12eV (I'm using Si as an example... it might not be Si but the orders of magnitude are mostly the same for most semi (check table above) ) would put the needed wavelength at 1.1micrometers (IR)
So if we fire enough photons of shorter or equal wavelength than say 1.1 micrometers (again,Si only an example) to overcome the bandgap we should make something that shouldn't be conducting at that moment temporary into a conductor which is more than enough to cause all sorts of craziness in there (current should be proportional to amount of photons (amplitude))
Also a Flash Lamp emits something in the order of magnitude of a MILLION lumens (www.wolframalpha.com/input/?i=1000000lumen) over a few micro-seconds and lumens are only measured in the visible light range! ...so according to the spectrum graph you've shown the peak in IR would be even greater ...that's a LOT of IR photons which are probably over the bandgap energy and are probably making a semiconductor into a "short" (whose conductivity is proportional to the peak amplitude of the light)...
What do you think EEVblog ?
Diego Spinola (but you can call me Bruce ;) )
I found this by accident 30 minutes ago...and Dave already made a video about this :)
I saw another chip near the hdmi that looks suspect. Perhaps it's a combination of the two?
joblessalex Yes there are definitely two of that kind of "chip package" on there.
There is something what im wonder about, at 19:53 when dave flashs the pi the last time i have the impression that the pi goes off some microseconds before the flash is flashing.
That's neat, I never really even thought of light being able to affect electronics to that extent, but it makes a lot of sense after you explained it.
Near IR has a lower frequency than visible light, so less energy than visible light. However, what's probably going on is that silicon is more transparent to infrared, so infrared light coming in through the back of the die can affect it.
There's a fair power in the uv though... It'd be interesting to take one apart and experiment.
Nope, the spikes are in the UV range and he has mislabeled the chart.
The fact that dim blue light produces a more pronounced photoelectric effect than bright red light was one of the clues that originally gave Einstein the insight into working out what was going on.
LiamE69 I think it's labelled properly (in nanometers). I did a quick image search for "xenon spectrum" and all of them have lower-frequency light (IR) on the right, as opposed to how RF spectrum is normally plotted. They also all show that xenon has spikes in the IR part of the spectrum, but not in the UV part.
I don't know how transparent silicon is to UV, but it is certainly transparent to (some?) IR.
Karl Koscher
I did the same and looked up the spectrum of xenon lights as you can see on a post elsewhere here. Yes the spikes are in NIR. As for labeling I simply cannot see any in my video. I could see the figures but not the unit. As he talked about frequency I had it in my head that it was the units were THz, but he does say it is nm.
That correction aside, it really is the UV doing it. The IR spikes will have a far smaller PE effect than the portion of the emissions in visible light which in turn will have a smaller PE effect than the portion of a xenon lights output below 400nm, which is small but significant.
InXLsisDeo
Yeah, been there corrected that. Still it doesn't change the fact that the PE effect is a threshold effect. NIR doesn't produce a PE effect on any material I am aware of. Visible light does on some materials. Near UV does on most metal and as it is produced by a xenon arc it is the culprit here. Very high UV and beyond produces a PE effect on anything but is not produced by a xenon flash.
Dave, silicon is transparent to IR light, right where PN-junctions starts to loose sensitivity. So photons to blame are between 1050nm and 1100nm wavelength: silicon is somewhat transparent there and PN-junctions are still slightly sensitive.
Hey Dave! The infrared part of the spectrum can't be the light causing the problems. Infrared light has a lower frequency than visible light. Remember that frequency is inversely proportional to wavelength.
I would have assumed RFI, from the high voltage supply of the Xenon power supply... looks like I am wrong, and not would have expected the photo effect, which you have clearly shown even by cutting apart the 2222A transistor. Thanks for demonstrating!
Dave can you place a 100uf or more cap near processor power line and try again ?
Hey Dave, love the video; I was wondering what the deal with this was. I have to nitpick the physics a tiny bit, though. You're saying "energy" or "amplitude" when "intensity" is more correct. Yeah, a higher number of photons can collectively have a higher total energy than a lower number of photons, but when explaining the meaning of that wavelength/intensity graph the word energy should be used only in reference to the wavelength axis, not the intensity axis.
analogous to a certain extent to volts, amps.
Wow i did not expect a Physics lesson in this video, i learned something new!!! thanks!!!
And you got a New Sub! keep up the interesting videos
So this IC screws up when hammered by photonic induction?
Maybe the high frequency pulse is the xenon trigger pulse and the second blip is the current through the lamp? you could check by measuring the time in between the pulses and comparing it to the time it takes for significant current to flow through a typical xenon lamp after it receives a trigger pulse.
Few years ago (back when I was just beginning with electronics) I did an experiment in which I have cut out the top of a TO-18 packaged transistor (just like you did) and stuffed IR LED inside. This way I've build working optocoupler. It was a crap but it worked.
This is awesome content. Awesome. Never thought it could happen in electronics. Changed my point of view for electronics.
At one of my collage courses ( measuring in electronics ) our profesor told us that IR spectrum of light is the most dangerous for semiconductors (i think we were doing something with " optocouplers " ) so this must be true! Thanks Dave for renewing my knwledge
It was probably said in a later video, but could it be that the Broadcom chip had browned out from the drop in voltage from the buck converter? And said brown out doesn't auto-reset it?
if possible could you revisit this? it looks like you actually covered some of the main arm chip as well when you covered it the second time. - cab you try just using a ir filter cut to fit the small chip or something else to confirm? obviously it seems like youve nailed it - but I am just curious. -murica
While I am not an expert, from what I have read I believe that this is an example of the photovoltaic effect, not the photoelectric effect as you say.
To quote WIkipedia: "Instead, as it turns out, electrons are only dislodged by the photoelectric effect if light reaches or exceeds a threshold frequency". But as you say in the video, the effect here is a result of the spikes in the infrared, and people testing with high-intensity visible light have generated no reaction.
As per Wikipedia, the photovoltaic effect doesn't have the same threshold. And it does occur in silicon, as it is the effect used for current generation in solar cells.
I see that you have put various extra text on the video, but e.g the one 10:26 talks about total energy, where if it was the photoelectric effect it would also have a requirement for individual photon energies. At 11:53 you also talk about a specific frequency, where the photoelectric effect works with lower threshold frequencies.
I do love the use of the classic Clive Sinclare solution to the problem.
Wow. Loved the explanation of the emp grounding spike :)
My Raspberry Pi 2 B arrived this morning. A full kit with it too. Here's hoping and fingers crossed. Before I start, should I ut a blob of black silicone over the ic?
Great, now i understood the effect eventually. It was always a mystery to me but with this life example i got it.
Thanks for the video Dave! If i had professors like you i would have 10 degree! :D
The energy needs to be above the work function for the material. So there isn't a *specific* wavelength that it works at, there's a boundary where it starts to work. Also uv is higher energy than optical and ir, so if the light enters from the side it'll probably be the uv.
"This is basic quantum physics" XD Made me smile. He said it like everybody in grade school should know it like an old star trek episode :D
Silly question - would a (bigger) smoothing cap on the output of regulated circuit mitigate the dip?
a big gob of blue-tack in your hand can be used to dab off the remainder of the goop on your board.
Thanks for the video - I totally thought it would have been the EM pulse from the high voltage discharge rather than the actual photoelectric effect. Brilliant!
Dave, you are awsome in all you're tubes videos. !! thankx
Most intriguing, wonder how much knowledge can a mind contain before it runs away rampant? Or perhaps evaporating much of what we learn to create space for more information? Either way I find it interesting how history, physics and electronics play a direct role in the scheme of things and yet wonder helplessly how much more information I need to store in my mind before I go totally bonkers, plus I still have neither bought myself a decent multimeter nor a bloody meager scope. I am definitely certain that all of us require a sort of calibration to weigh the value of the knowledge we attain for the sake of validating its virtue. I believe it is the character not the quantity of information, for those who are eager to learn then they will learn beyond any caliber or measure. Interesting video, thanks Dave.
I was wondering if you could do a class and build on the bedini fan circuit with cap pump and tell us how it works?
I've dealt with this effect a few times in 35 or so years, mainly with clear glass diodes injecting noise into analog circuits. While I believe that you have found the culprit, I would feel 100% confident (as opposed to 98%) if your test had also included the inverse test, (ie. masking everything but the I.C. in question). Still nice illustration of how a perfectly engineered product can be totally compromised by a little cost savings on a single I.C. device.
Where can I get the Physics Edition of Dave CAD? Looks like a useful add-on!
U16 is a problematic die level chip in the R-Pi2. My solution to this is to encase it with some black hot glue.
This chip should have been covered when it was put on the board but QC now-days is non existent it seems.
I have recreated the Xeon lock eccect by using different light sources from Xeon flashes to White Blue, and UV LEDs.
Another effect also exists with the pi and that's the EMP Effect from devices that emit RF such as a cell phone or 2-way radio which will cause the Pi to lock up also. There is no RF shielding on the Pi so all sort of stray signals can get in and cause the pi to malfunction. Solution for this is to shield the pi IF your using it as a control device for a wifi repeater node you want to shield it from the wifi RF.
Hi Dave it is common problem with micro controllers for example we have same problem with STM32L series when it ramp up with specific sloop rate it hang up and no WDG work even
have you considered that the light from the might might be trensferred through tha circuitboard it self, and actually shining light on the chip from underneath?
Using the red laser to attempt trigger (11:30):
"I can't get the damn sausage..."
:P I must start using this expression!
"Oh man, I'll never get that all off" Next shot... clean as a whistle!
Well done Dave, great explanation.
I remember seeing a thing in a ZX Spectrum magazine in the 80's about how to turn a memory chip into a camera to connect to your speccy, think it was a memory chip anyway, it was a long time ago.
Whatever happened with that huge train set you were rescuing from that closed down model shop, no updates on here ( i dont read the EEV blog )
Yeah, the explanation given is wrong. A large number of photons emitted by the xenon flash have a frequency that corresponds to the energy of the bandgap of the semiconductor material. When these photons are absorbed by the semiconductor, electrons jump from the valence band to the conduction band, resulting in current flow, which screws with the voltages in the chip.
InXLsisDeo I agree, you can't really know the wavelength that is causing the issue without isolating the bands.
InXLsisDeo BTW, I tried a UV filter and it made no difference, problem remains.
***** the smps chip might be self regulating for slowly (in most terms) ramping effects hence why bright light doesn't affect it, but the sudden immense pulse from the xenon flash is the quality, quantity and intensity slope required to break the regulation loop.
***** It has everything to do with the bandgap. The photoelectric effect is about electrons being given enough energy to escape from the surface of the metal (which we are only likely to observe in vacuum like Einstein's experiments were). This specifically relates to undoped materials, and the silicon in question is made up of doped p-n junctions. The photoelectric effect is slightly different theory to band gap physics. However, incident photons with energy greater than or equal to the band gap of the material will promote electrons to the conduction band from the valence band allowing current to flow. It's for this reason that silicon transistors become useless at high temperatures (Thermal distribution shifts to an emission spectra near the bandgap) because you end up with a large proportion of electrons in the conduction band effectively turning your transistor into a wire. Also, the intensity of the light doesn't have any effect on electron energy, but it does relate to the number of photons emitted.
InXLsisDeo Looking at the transmission spectra of silicon, it is about 55% transmissive at UV frequencies. So having said that, we can expect that roughly 45% of photons at a UV frequency are absorbed and will most likely contribute to any current generated or simply thermalise (shed excess energy through lattice vibrations/phonons) down to lower bands.
So, would it fix the problem if you would put some of that black stuff he showed around that tiny chip? And would you need a lot like from that blue stuff or would a small amount be fine?
I think you needed so much bluetack because there are 2 exposed chips on the board, the second one being right behind the HDMI port. You only eliminated the photo electric effect after you had covered both chips with blue tack.
This is of cause just a guess as to why you needed so much, what do you think?
Hi, I think there's another chip-scale package near the HDMI-Connector. It wasn't covered by Blue Tag on the first trial, but covered by Blue Tag on the second trial. Maybe that's the real culprit and not the switch mode regulator ?
Neat! The LED experiment was awesome.
Thanks for sharing this video. To remove blu tack use more blobs of blu tack over the part where you had ot covering the chip.
I am relitively newbie in electronics, but can you add a capacitor on that line to keep it stable and compensate that time the voltage drops down? At least theoretically am i right?
I've learned something.
Thank you, Dave.
So now I know what is that black dot on cheap electronics, thanks Dave! :D
is this the same thing that is supposed to brake out satellites if there is a big solar flare?
would putting some black tape over the exposed chip protect against this effect?
Hi All
Could the problem be in the circuitry used to drive the camera's xenon bulb - electrical impulse rather than a light/photon impulse issue?
This could explain why the blue putty didn't work . . .
What's that black goo officially called and where can we buy it?
hi can you check to see if the new > Raspberry Pi 3 < has the same flash problem please
raspberry pi was made after the problem was discovered... they fixed it by then
how could you done this great video and not cover it up correctly damn I was waiting for that.
13:19 how remove black glue?
Would an IR remote control be "bugger all" energy or does that lock it up too?
Hey Dave. Do you try to use a different multimeter every video? Every time I see you use a multimeter in a video it's different to the last one.
Great video!!!! Got my brain churning!!! Some further ideas come to mind: You could try a UV LED to see if it it UV energy. Another thought: Could the actual problem be the EM pulse from the photo-flash, not the actual light. I postulate this because the board reacted in a similar manner when flashed from behind.
would adding a fat capacitor after the regulator correct the problem ?
can you make your system crash by xenon flashing a decapsulated cpu like an i5?
Photogulously interesting Professor. Thank you
Ok, someone posted on FB that they took a flash picture of their 3D printer with their phone, and it crashed. Is it possible the "flash" on newer phones, a Samsung S10, is closer to a Xenon flash?
I like Dave's solution, put some blue tac on it!, it's reminiscent of the fix on the ZX81 Ram expansion module being loose and causing the ZX81 to crash. A kid used blue tac to solve the issue and Sir Clive himself demonstrated the blue tac fix at a trade show!
i wonder does turning lamb light on and off do same effect??
Photoelectric effect does not occur at wavelengths below red, the UV component in the xenon tube is most likely to confuse the chip.
actually... I think you're only thinking about the classic photoelectric example of ripping of electrons from the metal surface(work functions)... However the Bandgap energy on semiconductors allows for much lower energy photons to be causing charge carriers (free electrons in the lattice) to "appear" and thus make a semi-conductive junction to ...well... conduct when it shouldn't
if you take the bandgap for pure Si 1.11eV (as an example... the doped junction in that IC has probably a lower bandgap still) and compare it to it's work function 4.60eV you'll see that IR and visible light CAN cause it to conduct when it shouldn't (so yeah, not because of positive "carriers" but negative ones)
Diego Spinola yep...that's actually true...i remember cracking old TO-3 packages and measuring that the die produced current when exposed to light...still an interesting problem...I would be curios to see what happens if one shines an uv LED straigt into the chip, though
No, no, no! Dave, please, don't explain something simple like this the wrong way! D: The energy of the photon is E=hf, meaning that a higher frequency will put more kinetic energy into the electron, increasing *voltage*. The number of photons, however, determines the number of emitted electrons, which increases *current*. There is also not a specific frequency required in order to emit an electron, it's a *minimum frequency*.
The infrared spikes in the xenon spectrum would therefore (if they are above the minimum frequency at all) create a spike in current, but it would be at a very low voltage compared to the electrons emitted by the photons of visible frequency.
nRXpAa8E6UML Yes, I was implying minimum frequency. This will depend upon the semiconductor doping.
So Dave if I blob black epoxy over the culprit chip, would that fix this issue?????
can you fix it by putting a blob of nail polish on there?
or will nail polish damage the board?
Great explanation. Learned a lot!
It might be the IR as you mentioned. Silicon is transparent to IR. It probably is not getting to the chip from the underside. It is probably going right through the top face. Thanks for the excellent video. On a side note radio shack black plastic project boxes are somewhat transparent to IR as well.
Would it be possible to add a Capacitor so that when the regulator drops out the cap provides power for the few ms it takes to recover? I understand that's not best solution, preventing it from happening would be better, but could it be an option, perhaps for people who want to bodge something in there...
How much for DaveCAD?
I was thinking of buying one of these to run as a media centre. But I really dislike Kodi, something about it irks me the wrong way and I hate using it. Better options?
Quick question out of curiosity. If the regulator is recovering so quickly could the problem also be solved by more decoupling caps on the inputs to whatever is locking up?
aftertwotoo Perhaps, but that would be a poor fix, as you shouldn't rely on the regulator to recover from such a thing. Much better to simply stop the problem from happening in the first place.
How did you rule out the emp pulse from the flash electronics as the cause?
If the EM pulse was the cause the problem would've continued after covering with Blu-Tack
Yep, but it clearly blocked it. I wonder if black enamel paint would work.
Adding to that, the HF spike he mentioned was from the loop of ground.
I assume he meant the flash cap dumping all the current made some RF.
The light gets under the balls.
Where the sun don't shine I suppose???? Had me laughing too hard!
Does this effect work also when Raspberry Pi 2 is inside the case?
The breadboard is still set up for the voice recognition chip!
cool! this should have been a fundamental Friday.
now i am wondering, redoing all of the board is not an option. A blob of "blackness" could do the trick. But you showed that there is a drop in power during that flash and the processor stops working. What if they put an elco ( or how it is called in english ) in that spot so that there won't be a drop in power.
Theoraticly the processor could be working all the way through while the power regulators recovering and bringing all back to normal. Could that also do the trick?
Oh great. You upgraded DaveCAD to the Physics Edition. Good choice.
The shorter wave the more energetic it is. Photoefect equation.
Если кто-то застал те времена, когда в старых микросхемах BIOS было заклеенное скотчем окошко на кристалл. Информация CMOS сбрасывалась путем подачи света в окошко на микросхеме, а не перемычкой как сейчас -)
Never tough I would see bearchip with out plastic package, especially BGA...
Just wondering if its possible to make video for LIN and CAN communication's. Would be nice because they are widely used this days in many communication systems and mostly in the automotive manufactures. I can make video of my own but I doubt it would be any close to the level of your videos Dave. Anyway keep up the good work!
P.S. Raspberry rocks I use one to run my home FTP server and wake up by the network my home mighty xeon server that I run ESXI and some unix and linux virtualized OS systems on it. Saves a lot of energy rather running that server 24/7, just waking it up when I need it :) And the raspberry consume only like what 5w/h?
Hi! Nice to see you got the new Raspberry Pi 2 Model B. I love it!
I got one myself. I have experience with the Raspberry Pi and blog tutorials to get started with it!
I also blog Arduino, C/C++ - Tutorials and projects I make.
I am so sorry for this self advertising, but my blog is fairly new and I would love to see you on my blog. I might help you. But for now… I follow you!
Thanks for reading!
Forgot the link: howtoelectronic.wordpress.com/
I just started the blog. The tutorials will follow soon! Thank you again for reading!
So this photoelectric phenomenon makes current go backwards on the diode?
HUGSaLOT Valkyrie It is electron current flow, not conventional current flow.
How do I get a license for DaveCAD Physics Edition?
Thanks for explaining, cause my physics edition license expired on DaveCAD
I heard "Balls under there" and "Balls in there" so many times, i even started to look down a few times..